The I Kissed A Girl singer is finding it ‘therapeutic’ to channel her rage into her songwriting her fourth studio album.

A source told Grazia magazine: ‘Katy goes from being angry one minute to upset the next. And she really is laying everything out there in her music, which she says has been extremely therapeutic.

‘This new album will certainly be explosive.’

Perry shocked the audience at the Grammy Awards earlier this month when she performed ET and a new song called Part of Me, which seemed to include furious lyrics aimed at her ex-husband Brand.

She sung: ‘You can keep the diamond ring. It don’t mean nothing anyway.’

Katy added:’You chewed me up and spit me out / Like I was poison in your mouth’ and ‘You ripped me off, your love was cheap / Was always tearing at the seams’.

The source said Perry’s best friend Rihanna backed her performance.

‘Katy’s performance was intended to stick two fingers up at Russell. Her best friend Rihanna fully encouraged it, too.’

Perry is reportedly furious that Brand appears to have moved on quickly from their divorce – which was made final on February 8 – with rumours that he has a new Mexican girlfriend called Oriela Medellin Amieiro.

‘When they signed the divorce papers, it was upsetting but fairly amicable,’ the source told the magazine.

‘Now it seems Katy has gone into the next stage of grieving and, with all these rumours about new women, she’s mad as hell? Katy is furious with Russell for not trying to save their marriage. He broke her heart and it’s only natural if she wants him to suffer pain like she has.’